1. Field of the Invention
This invention relates generally to a planetary gear unit for an automatic transmission, and more particularly to an assembly that includes a planet pinion carrier connected to a powdered metal plate of a one-way clutch.
2. Description of the Prior Art
A conventional Ravigneaux gearset includes a carrier containing two sets of planet pinions, long pinions and short pinions. Each pinion set includes several pinions. Each pinion is mutually spaced angularly about a central axis, each short pinion meshing with a corresponding long pinion. There are two sun gears, a short sun gear meshing with the short pinions, and a long sun gear meshing with the long pinions. A ring gear meshes with the long pinions.
Both planet pinion sets are supported for rotation on the carrier. Each long pinion is in mesh with a short pinion, the ring gear, and the long sun gear. Each short pinion is in mesh with a long pinion and the short sun gear.
Ravigneaux gearsets are used in many automatic transmissions due to their compact size. A Ravigneaux gearset can be used in lieu of two simple planetary gearsets to produce four forward speeds and a reverse gear. They are smaller, and require fewer components than two simple planetary gearsets because they have one ring gear, and one carrier. Their manufacturing and assembly costs compare favorably to those of simple planetary gearsets.
Frequently a Ravigneaux gear unit is controlled by a hydraulically actuated friction brake, which alternately holds the carrier against rotation on a transmission casing and releases the carrier to rotate freely. A one-way clutch is often arranged in parallel with the friction brake between the casing and planet carrier. The rings of the one-way clutch are formed from powdered metal, but the other components of the carrier assembly are machined from cast iron. There is a need to integrate such one-way clutches into the carrier assembly using mechanical connections. But the components of the integrated assembly that are fabricated from powdered metal and those that are fabricated from cast iron have substantially different material stiffness and strength properties. For example, pinion carriers are less expensive, more rigid and have better pinion window tolerances when made from cast iron than from powdered metal. The joint between a cast iron carrier and a powder metal clutch ring must radially locate both parts, axially retain both parts, and carry torque. Conventional methods for joining the two dissimilar materials include a spline and a snap ring, but these require excessive axial space; a shearing spline, which would create high radial loads on the thin powder metal clutch ring; or a press fit, which would not carry the high loading.
There is a need in the automatic transmission industry for an integrated carrier assembly comprising both a one-way clutch of powder metal and other components of machined cast iron that overcomes these and other problems associated with integrating and mechanically joining the dissimilar metals.